Low melting oxide glass



Oct. 29, 1968 M. E. oumeswu. 3,408,212

LOW MELTING OXIDE GLASS Filed June 4, 1965 100% 50% 100% PbO or 0 Pb 2 (MQLE PER CENT) MAURICE E. DUMESNIL I NVEN TOR.

A T TORNEY Un t d msPate LOW MELTING OXIDE GLASS Maurice: E'. Dumesnil, Palo Alto, Calif., assignor to F airchild Camera and Instrument Corporation, Syosset, N.Y., a corporation of Delaware Filed June 4, 1965, Ser. No. 461,325 6 Claims. (Cl. 106-47 ABSTRACT OF THE DISCLOSURE A composition consisting essentially of a combination of V 0 PbF and either-PbO or T1 0, the proportions being selected as described so as the composition will form a glass without need of additional components;

The invention relates to a low melting glass composition particularly useful for the encapsulation of semiconductor devices. More specifically, the invention is directed to a glass composition containing V 0 PbF and an oxide of a metal selected from the class consisting of Pb and Tl as its primary components.

Medium and high melting glasses (e.g., melting points above 600 C.) have long been well known in the art. US. Patents 2,946,704 and 2,949,376 show such conventional glass enamels. These enamels contain large proportions of what are traditionally termed glass formers, such as SiO and E 0 in combination with other oxides. It has long been established in the art that the presence of these glass formers is what makes it possible to maintain an amorphous state. Without them, no oxide glass can be formed. 1

The above glass compositions have a serious disadvantage in thesemiconductor industry where'a glass melt ing in the range of 250 to 400 C. is most desirable for encapsulation of semiconductor devices. The melting points of these prior art glass compositions are normally in excess of 420 C. Furthermore, as an additional restriction, these glasses must match the thermal expansion rate of the metal leads used on the semiconductor device, and must possess no components which are deleterious to the underlying delicate semiconductor device.

Contrary to the normal requirements established in the art, a new glass composition has been discovered which contains none of the conventional glass formers, such as B 0 and SiO;, This new glass composition has a melting point in the range from about 250 to 400 C., making it highly desirable for use in semiconductor device systems. The composition contains no components deleterious to semiconductor devices, and achieves a glass which is thermally matched to the metal leads. Briefly, the glass composition of this invention contains at least 75% by weight of a combination of V 0 and oxide of a metal selected from the class consisting of Pband T1, and PbF (the amounts of each of these components being selected from within the enclosed curve shown in FIG. 1). The resulting glass compositions not only have a desirable melting point and the ability to thermally match metals in the thermal expansion range of 7 to 10 per degree Centigrade, but also are relatively free of cracking and are able to stand temperatures up to about 200 C. without any undesirable side effects. These glasses become fluid in the range of about 280 to 400 C., so that silicon semiconductor materials, including, for example diodes, transistors, and microcircuits, may be embedded in the glass without deleteriously affecting their properties. This is particularly important with respect to silicon-metal systems, such as silicon-gold, which has a eutectic point of 380 C., and metal systems such as aluminum-gold, which interditiuses rapidly at temperatures above about 350 C.

3,408,212 Patented Oct. 29, 1968 The details of the glass compositions of this invention will be more fully set forth below, with reference to the single drawing which shows the range of compositions of the three primary glass components useful in this invention. a

At least 75% of the glass composition of the subject invention should be selected from a composition mixture shown inthe drawing within the enclosure 20. Selecting point 21 on the graph, for example, it is apparent that at least 75 of the glass mixture at point 21, within the scope of this invention, has the following composition: 55% V 0 25% PbO or T1 0 and 20% PbF Apreferred glass composition of this invention contains from about 40 to 70 mole percent V 0 10 to 40 mole percent PbFz, and from about 20,to 40 mole percent of an oxide of a metal selected from a class consisting of Pb and T1.

In addition, the glass composition may have an additional 0.5 to about -mole percent A1 0 Furthermore, the mixture may contain up to about 30% P 0 up to about 5% ZnO, 8% ZnF and up to about 8% BaF B30, SlFg, SrO, C3122, C30, M003, R1320, c520, W0 or Ag Each of these additional materials, either aloneor in any combination with the other materials, improves the chemical stability of the glass. With these materials included in the glass composition, the likelihood of devitrification, which is undesirable in the glasses of this invention, is greatly reduced.

Without intending to limit the scope of the invention, as set forth in the appended claims, there are certain preferred glass compositions which have been found to have excellent properties for the purposes of this invention. They are therefore set forth below.

EXAMPLE I A glass having the following composition was prepared by melting in a platinum crucible:

V 0 mole percent) 333i PbO, (20 mole percent) 20.8 PbF (40 mole percent) 46.0

A black glass resulted which softened at 250 C. and was extremely fluid at about 280 C. Silicon devices were encapsulated in this glass which remained stable for hundreds of hours under the conditions of high humidity and high operating voltages.

EXAMPLE II The composition was the same as Example 1 except thallium oxide was used instead of Pb(). The softening point also was around 250 C., and the other characteristics were similar to Example I.

EXAMPLE III Compound: Percentage PbO 28.5 V 0 Zn() 4 PbF 10 M003 5 BaO 5 P 0 1.5

and annealing temperature are such that the glass will form a good seal to the majority of metals with widely varying linear thermal expansions used as contact or interconnection materials on semiconductor devices. If desired, the softening point of this glass can be widely varied from about 350 C. to 500 C. by merely increasing the P content to increase the softening point.

A series of glasses were manufactured using the mole percentages of V 0 set forth in the following table (the numbers correspond to compositions shown on drawing):

TABLE I Number on Mole Percentage Drawing Softening Point V205 PbO PbFg P205 20 0 270 C. 20 0 270 C. 40 0 250 C. 0 35 0 N 0 glass (outside scope of invention).

35 8 go. 50 0. 20 0 Do. 10 0 0 400 C.

..... 0 Glass devitrified readily in 5" 3 remelting.

38 5 290 C. 36 10 320 C. 35 15 340 C.

Each of these glasses, with the exception of numbers 5-9 as noted, performed satisfactorily for the purpose of this invention. Numbers 5-9 are not glass compositions within the meaning of that term as applied in this specification.

The above description and specific examples merely illustrate preferred embodiments of the invention. Therefore it is the intent that the scope of this invention be limited only as expressly recited in the claims which 3 follow.

What is claimed is: 1. A glass composition consisting essentially of a combination of V 0 PbO, T1 0 and PbF the amount of each of these components being selected from within the enclosed curve in the drawing.

2. A glass composition consisting essentially of from about to mole percent V 0 10 to 40 mole percent PbF and 20 to 40 mole percent of an oxide of a metal selected from the class consisting of PhD and T1 0.

3. The glass composition of claim 1 having in addition from about 0.5 to 35 mole percent A1 0 4. The glass composition of claim 1 having in addition a minor amount less than about 8 mole percent of at least one compound selected from the class consisting of ZnF BaO, BaF SrO, SrF MgO, CaO, CaF MoO ,'WO Ag O, Cs O, and Rb O.

5 A semiconductor device comprising a semiconductor material having a coating of the glass of claim 1.

6. The glass composition of claim 1 having in addition up to about 5% ZnO.

References Cited UNITED STATES PATENTS 2,853,393 9/1958 Beck et al 106-47 3,115,415 12/1963 Hoffman 10649 3,149,234 9/1964 Hood et a1 10647 3,200,310 8/1965 Carman 317-234 3,211,826 10/1965 Holcomb et a1. 106-49 3,241,009 3/1966 Dewald et'al. 3l7-234 3,278,317 10/ 1966 Blair et al. 106-47 FOREIGN PATENTS 744,205 2/ 1956 Great Britain. 165,870 11/ 1964 U.S.S.R.

OTHER REFERENCES Fajans et al.: Stability of Lead Glasses and Polarization of Ions, I. Am. Cer. Soc., vol. 31 (1948), pp. 113- 114.

HELEN M. MCCARTHY, Primary Examiner. 

